1. Field of the Invention
The present invention relates generally to semiconductor devices, Micro Electro Mechanical Systems (MEMS), sensors and more specifically to three dimensional (3D) three-axis force sensors integrated with signal processing electronic circuits on one substrate. In particular, it relates to three-axis finger force sensors, finger-mouse and micro-joysticks for consumer and other applications.
2. Background
3D force sensors based on micro-machined silicon chips with stress sensitive components on flexible diaphragm are known. Prior art shown in FIG. 1, uses a sensor chip 10 from a rigid frame 12 and rigid central part 16 of a die, boss, connected with the frame by a thinner diaphragm 14. An externally applied force is transferred to the rigid island 16, the deflection of the island creates deformation and stress in the elastic diaphragm element 14, reaching the locations of the stress sensitive IC components 18, 20, 22. Because the rigid island 16 is located within the thickness dimension of a die 10 and the width of a circular diaphragm is small and in the sub-millimeter range, it is very hard to apply external forces in lateral X and Y directions to the rigid island 16 to provide good response, and hence their use is constrained from many consumer devices and interfaces.
In order to resolve this deficiency a rigid force-transferring element 31 is added to the structure of the die 10 and island 16. This rigid force-transferring element 31 is firmly coupled to the rigid island 16 of a sensor die 10 through intermediate layer 33. This extension of the rigid island height above the die frame thickness enhances sensor sensitivity to the applied vector force in all orthogonal directions. These components of force are transferred to a rigid island of the sensor die and then to the elastic element and sensitive IC components.
However, the disadvantages of these kinds of solutions are the requirement of additional wafer for the rigid force-transferring elements, additional micro-machining, aligning and bonding two wafers, a more complicated process of separating dice from the wafer and generally a more expensive fabrication process.
What is needed are devices that reduce cost of fabrication and manufacture as well as providing an easy integration with the higher density IC circuitry on silicon substrate.